Sulfonic acid cation exchangers containing amine groups



United States Patent O 3,370,021 SULFONIC ACID CATION EXCHANGERS CONTAINING AMINE GROUPS David Harry Kuhn and Abraham Schwarz, Haifa, Israel, and Kurt S. Spiegler, Glastonbury, Conn., assignors to Technion Research and Development Foundation Limited, Haifa, Israel, a corporation of Israel No Drawing. Filed Nov. 7, 1963, Ser. No. 322,024 2 Claims. (Cl. 260-2.2)

The present invention concerns ion-exchange resins.

More particularly, the invention concerns resinous cation exchangers. In the following specifications and claims the terms ion exchange resin, resinous cation exchanger, cation exchanger and the like will be used irrespective of the mechanism by which the cations are retained by the resin and exchanged for other cations.

It is the object of the present invention to provide new cation exchangers of improved properties.

A cation exchanger according to the invention is obtained by nitration of a synthetic resinous polymer or copolymer that contains acidic groups and, if desired, reduction of the resulting nitro polymer into the corresponding amino polymer.

The starting polymer or copolymer used for the production of a cation exchanger according to the invention may already be a cation exchanger per se, in which case its modification in accordance with the invention serves for improving some of its properties such as, for example, its selectivity towards a certain cation, its reactivity or the like. The acidic groups of the starting polymer or copolymer, which are retained in the final product, may for example be sulfono or carboxy radicals. Examples of starting polymers and copolymers are sulphonated polystyrene, sulphonated styrene-divinylbenzene copolymer, sulphonated phenol-formaldehyde resins, various resins with carboxy group and the like.

It has been found that in accordance with the invention it is possible to prepare cation exchangers that are selective in their cation affinity so that these exchangers are suitable for use for the selecttve removal of certain cations from solution in preference to the other cations present in the same solution.

It is known that even conventional cation exchangers exhibit a certain degree of selectivity in their cation affinities. For example, most of the conventional exchangers will exhibit a slight preference for the retention of potassium over sodium. Furthermore, between cations of different groups of the Periodic Table those of higher electrostatic charge, that is to say of higher valency, are as a rule retained by the cationic exchanger in preference over cations of a lower charge, i.e. a lower valency. However, these selectivities although they are distinctly discernible are often too moderate to be of any practical value. In view of this, attempts have already been made to produce cation exchangers of specific selectivities. Thus for example according to US. patent specification No. 2,619,404 a K-selective cation exchanger is prepared by nitrating polystyrene, reducing the resulting nitro-polymer, reacting the resulting amino polymer with picryl chloride and further nitrating the product of this reaction. This sequence of reactions can be represented by the following reaction scheme:

EN 03 NaQSX picryl 0 150C chloride N0 NH:

As can be seen the final product contains as reactive, cation-retaining groups dipicryl amine radicals. Since it is known that the potassium salt of dipicryl amine is very scarcely soluble, the potassium selectivity of a resin containing a multitude of dipicryl amine radicals was-to be expected. Moreover, the multitude of steps necessary for the preparation of this K-selective resin seems to render the final product expensive and therefore useless for practical purposes.

It was therefore surprising to find that improved cation exchanger resins of specific cation selectivities can be prepared from acidic resins in ,a single nitration operation followed, if desired, by reduction of the resulting nitro resin into the corresponding amino resin. The cation exchangers are obtained in this manner in a high yield and the specific selectivities which they exhibit are of an order which renders their application for the selective removal of specific cations from their solutions practical and economical. The nature of the specific selectivity, the rate of exchange and the separation factor depend on various factors such as the nature of the starting material, the conditions of the nitration and the pH at which the exchange reaction is effected.

It should he noted that the nitrated and aminated cation exchangers according to the invention are of a different nature than the known K-selective exchanger described above. Whereas the latter includes, as already mentioned, as sole reactive groups a multitude of dipicryl amine radicals and the K-preference of the exchanger is based on the known aflinity of the dipicryl amine to potassium, the exchangers according to the invention contain nitro groups and/ or amino groups together with acidic radicals and the cation retaining capacity of the exchanger is accordingly based on a different mechanism.

The invention is illustrated by the following examples without being limited thereto.

Example 1.Preparation of a. K-selective cation exchanger from styrene-divinylben zene copolymer sulphonic acid (Amberlite IR 120Trademark) In a three-necked flask, provided with stirrer, thermometer and dropping funnel, g. of the above air-dried cation-exchange resin in its H-form was treated for 10 hours with a nitrating mixture composed of 1400 g. of H 80, and 350 g. of 90% HNO at various constant temperatures as given in Table 1 below.

After completion of the reaction, the granular product was separated from the reaction mixture. The product was neutralized with a 25% by weight aqueous solution of NaOH and water was added. The resin, which was dark coloured in its Na-form, was washed several times with water and repeatedly transferred from its Na-form to its H-form and back to its Na-form with 2N HCl and 2N NaOH, respectively. This procedure was repeated until the NaOH washings became colourless and free from any yellow colour. The yield in each batch was about 85 g. of nitrated resin.

3 The results obtained with three different batches at different temperature are summarized in the following Table I. In addition to the chemical analyses of the products as given in the table, the presence of NO -groups was confirmed by infrared spectra. The structure of the nitrated resin was about as follows:

when the potassium mole fraction in the solution is decreased to 0.1. It is thus seen that the K-selectivity of the nitrated resin prepared in accordance with the example is considerably improved.

(b) Na-K exchange.The nitrated cation-exchanger in its Na-form was brought into equilibrium with a solution (|3 HCHz-(3HCHz HCHi- (|3HCH: S03H @NOQ \NO:

| l 1 NO 2 S 3H N O 2 NO 2 TABLE I Reaction Tempera- Weight percent of element in the dry resin in its H-form N o. of experiment time, hrs. ture, C.

Carbon Hydrogen Oxygen 1 Sulphur Nitrogen 1 Determined by chemical analysis.

Qh=Exehange capacity in milliequivalents per gr. of dry resin as determined by tritation with KOH.

The nitrated resins obtained in this manner were found to be of a pronounced K-selectivity. This was established by the following experiments:

(a) Potassium-hydrogen excha rzge.The H-K exchange of the nitrated resins was studied on the reaction RH+K RK+H using aqueous solutions of KNO together with HNO at constant anion concentration of 0.1 molar. Four different solutions were used and these were introduced in four identical vessels containing the same amount of the same resin in its H form, The result of the experiments under equilibrium condition are summarized in the following Table II:

where Y and X are, respectively, the mole fractions of K and H in the resin, and X and X are, respectively, the mole fractions of K and H in the solution.

In contrast to these results the non-nitrated Amberlite IR 120 resin serving as starting material in the production containing equimolar quantities of NaNO;; and KNO (total cation concentration: 0.01 mole).

After completion of the exchange reaction, the resin was analyzed for its Na and K content. The result showed enrichment of K in the resin by a factor of 2.2 (i.e. it contained 2.2 more K than Na).

For comparison, the Amberlite IR 120 cation-exchange resin has a factor of about 1.4 whereas a resin of the dipicrylamine-type has a factor of 2.7.

The rate of the cation-exchange was of the same order as of Amberlite IR 120.

EXAMPLE 2.Reducti0n of the nitro-resin obtained according to Example 1 The reduction of nitrated polystyrene-sulphonic acid was carried out with SnCl in HCl-solution. This method ensures the selective reduction of the NO -groups to -NI-I only without simultaneous reduction of the SO H-groups or the aromatic rings.

The reduction was carried out as follows: The nitrated polystyrene-sulphonic acid (20 gr.) in its H-form, having an N-content of 7.93% (0.113 mole) was added to a solution of SnCl .2H O (115 gr.; 0.51 mole) in concentrated HCl (400 gr.) and the mixture refluxed while stirring for ten hours. Then the solution was decanted off and the solid material left washed with diluted HCl (2N) until no more SnCl appeared in the effluent. Thereafter the resin was repeatedly transformed into its Na-form and back into its H-form and washed with water, until no more chloride was detectable. The pH of the wash water at this stage was 4.9. The resin was dried over P 0 Yield: 15.5 gr.

As starting materials, the three difierent resins of Example 1 were used and the result of the chemical analysis of the product is summarized in the following Table 111 TABLE III Resin Carbon, Hydrogen, Chlorine, Oxygen 1 Sulphur Nitrogen percent percent percent Cation-exchange resin 2 5. 14 30.05 15.09 0. 13 Nitrated e.e.r. 44. 01 3. 51 36. 82 7. 58 7. 93 Above nitrated resin after reduction 52. 42 5. 2.08 20. 17 10. 02 8. 79

1 Determined by chemical analysis.

2 Starting material. Exp. No. 3 Table 1.

of the nitro resins as specified hereinabove manifests a K-selectivity at a potassium mole fraction of 0.95 in the solution, and a quantity of an ion A in resin Xvolume of solution in mi.

weight of dry resin in H-form Xquantity of ion A in solution where A is the ion that is being exchanged.

TABLE VI Starting concentration of Cu++ in solution. 5x10 M 5X10 M Ionic strength in solution 0. 090 M 1 M pH 5.60 5. 52 K1 2, 502 a, 450 Percent Cu++ removed 1 from solution 98 1 Minimum value.

The cation exchangers of the present invention also excel in their rate of ion exchange. This is demonstrated for example by one following experiment:

The aminated resin prepared as indicated hereinbefore is treated with a solution containing 3 l0- mole/litre of Zn ions and having a pH of 4.50 to 4.70. After 5 TABLE IV Starting Concentration Cu++:1 10- M Cu++:5X10- M pH 1. 70 2. 3. 55 4. 5. 75 1. 72 2. 43 3. 45 4. 30 5. 0 5. 95 Ionic Strength of solution 0. 065 0. 055 0. 050 0. 065 0. 090 0. 065 0. 055 0. 050 0. 065 0. 080 0. 100 Kd l 4. 92 29. 2 527 2, 060 2, 050 4. 92 18 159 538 1, 160 2, 360 Percent Cu++ removed from solution 1 0.0 30 85 95 95 4. 4 18 62 88 96 96 I TAB LE V Starting Concentration N i :1X10- M Ni++z5 10- M p 1. 75 2. 3. 70 4. 49 5. 22 5. 95 7.10 8. 02 9. 1. 80 2. 52 3. 61 4. 45 5. 15 5. 88 6. 4O Ionic Strength of solution. 0. 065 0. 055 0. 050 0. 065 0. 080 0. 090 0. 100 0. 090 0. 060 0. 065 0. 055 0. 050 0. 065 0. 080 0. 090 0. 100

a 1 4 4 312 393 2, 672 2, 660 2, 720 2, 370 7 32 77 185 322 673 1, 098 Percent Ni++ removed from solution 1 4 4 40 99 99 99 99 6 13 42. 2 66 76 86 92 1 Minimum value.

As can be seen from the foregoing tables, K; for copper at pH 3.55 is 527 whereas K for nickel at pH 3.70 is only 70. It can thus be concluded that at this pH range the aminated resin exhibits a pronounced preference for copper over nickel, the

being approximately minutes 75% 0f the Zn ions present in the starting solution were bound to the aminated resin. A corresponding experiment was carried out under the same conditions with the same solution using Dowex A-l (trademark) resin. In this case the binding of 75% of the Zn to the resin took 60 minutes.

What is claimed is:

1. Resinous cation exchange substances taken from the class consisting of polystyrene and copolymers of styrene with divinylbenzene, said substances containing a plurality of sulfonic radicals, said substances containing a plurality of amino groups, and being substantially free from water.

2. A method of exchanging cations comprising providing a material as set forth in claim 1, passing an acid aqueous solution of an ion to be exchanged into contact with said material sufiiciently to cause said ion to be attached to said material.

References Cited UNITED STATES PATENTS 4/1952 Skogseid 260-2.l 6/1966 Frilette 26079.3 

1. RESINOUS CATION EXCHANGE SUBSTANCES TAKEN FROM THE CLASS CONSISTING OF POLYSTYRENE AND COPOLYMERS OF STYRENE WITH DIVINYLBENZENE, SAID SUBSTANCES CONTAINING A PLURALITY OF SULFONIC RADICALS, SAID SUBSTANCES CONTAINING A PLURALITY OF AMINO GROUPS, AND BEING SUBSTANTIALLY FREE FROM WATER. 